The present disclosure is directed to an improved water blasting system, and in particular a water blast system capable of providing more narrow or focused streams of water in a water blast apparatus. This is accomplished with an improved nozzle construction. The present disclosure is directed to an improved water blasting system, and in particualr a water blast system capable of providing a more narrow cohesive stream of water in a water blast jet. This is accomplished with a combination of improved constructions including a pre-nozzle assembly, the nozzle orifice and a post-nozzle assembly. These and many other features will be set forth in the context of the water blast system described below.
Water blasting can be used for surface cleaning, or product cutting. Surface cleaning is exemplified by the problem of removing accumulated slag collected on the wall of a furnace. In this representative problem, a coating of furnace generated debris such as fly ash, cinders, silica, perhaps with metal constituents, will collect on the walls of the furnace. Similar accumulations can be observed in practically any processing system where the materials undergo processing confined in a furnace, reaction vessel, tower and the like. The accumulation of material inevitably reduces the efficiency. To restore the furnace or other equipment to an original, like new condition, the surface must be cleaned, and in some instances, this requires removal of materials which are almost as hard as the supporting surface, referring to the furnace, pressure vessel or tower which is coated with the undesirable material.
There is a similar removal problem which involves water blasting to remove a surface coating. For instance, a surface might be coated with paint, veneer, ceramic, refractory or the like, all intentionally placed thereon. Ultimately, the surface requires refurbishing or refinishing and to accomplish that replacement, the surface must be cleaned until clean metal shows, that is, the coating must be completely removed to uncover the supporting structural member.
Another common application of water blasting is the partial removal and/or demolition of concrete or other composite materials from roadway, parking structures, and/or runways, dams, locks, buildings and other similar concrete structures. A representative example of this problem is the requirement to remove weak and spalling concrete from piers supporting an elevated roadway. The concrete of the surface of the piers will deteriorate due to salt induced corrosion of the reinforcing rebar. To repair the piers, it is necessary to remove weakened concrete from above the corroded rebar. It is also desirable to remove additional concrete from behind the rebar to provide newly applied concrete with firm anchoring to the existing structure. At the same time, it is desirable to remove all rust and corrosion from the rebar surfaces. Water blasting is sometimes used for this task. In other circumstances, it may become necessary to remove concrete, stone or other hard material surfaces for the purposes of demolition, removal or modification. High pressure water blasting has application to such requirements. It has been discovered that typical road surfaces exposed to salt for deicing have an aging problem which is best handled by removal of the top few centimeters of roadway. For instance, in northern regions, rock salt is used to melt ice which accumulates on roadways, bridges, runways for aircraft, and the like. Small fissures in the concrete become saturated with the salt which ultimately attacks the integrity of the structure, thereby requiring periodic replacement. In a runway which is perhaps fifty centimeters thick, it is not uncommon to remove the top ten centimeters of the surface. Indeed, a desirable technique is to remove the top portion and expose the underlying rebars. Typically, the salt water penetration into the fissures will ultimately attack the rebars, forming a rust coating thereon and resulting in severe damage to the concrete structure. A loss of strength may also be noted because the rebars are materially weakened. New cement is poured over the surface to restore the thickness to the initial or desired thickness where the newly poured cement becomes an integral part of the structure. Bonding between the new and old concrete is important, and bonding with the rebars is likewise important. In this procedure, it is necessary to remove the top layer of the concrete, expose an interface which is irregular and suitable for adherence, clean the rust or other materials from the rebars to expose them to bright metal, and subsequently to pour the new cement in place.
In the representative cases described above and others too numerous to mention, current water blasting techniques suffer from several drawbacks such as (1) poor mechanical efficiency; (2) relatively short effective distance from the nozzle; (3) inability to cut or remove foulants, coatings, etc. at reasonable pressures, and; (4) slow work rates.
Numerous technologies have been adopted to address these shortcomings and include:
1. Addition of abrasive to the water blast jet. PA0 2. Addition of polymers or other viscosity modifiers. PA0 3. Use of pulsating nozzles. PA0 4. Use of higher water pressures.
Addition of abrasives increases the aggressiveness of the water jet; however, the added expense of the abrasive and the additional need to clean up the spent abrasive must be considered. In addition, abrasives added to water jets often become excessively erosive causing damage to nozzle components and the surfaces being cleaned and cutting or otherwise damaging rebars in situations where concrete is to be removed.
Polymer addition has also had some success in limited applications. The increase in water viscosity improves water jet cohesion, however, it suffers due to the cost of the polymer and contamination and disposal problems. Typically these drawbacks outweigh the minor improvement in jet efficiency. The effectiveness of the polymer is often substantially reduced when the polymer chains are sheared under conditions of high shear and turbulence within the nozzle.
Pulsation nozzles which generate short periodic bursts of water also seem to give some increase in mechanical efficiency. Although this technology has received much academic attention, it has achieved only limited commercial acceptance. This technology is relatively expensive to achieve and is subject to mechanical wear of nozzle parts due to cavitation.
Use of higher pressures has had the most commercial success. Water at pressures of 1,380 to 2,400 bar has improved mechanical efficiencies and work rates without addition of contaminants. This technology has not, however, increased effective working distance appreciably and the costs associated with the purchase, operation and maintenance of 1,380 to 2,400 bar equipment is high.
The present disclosure is directed to an improved distribution system including a nozzle and mounting mechanism for the nozzle as will be set forth. An entire system is disclosed. Focusing for the moment on the nozzle, a typical application requires a strong structure at the nozzle having thick side walls, a relatively large chamber within the nozzle and an orifice attached to the nozzle for delivery of water flow out of the nozzle chamber. Moreover, this nozzle delivers a more narrow stream which cohesively stays focused for a greater distance. There is a tendency for the stream to change from a narrow, focused, precisely shaped stream to a divergent scatter of droplets farther from the nozzle. This can be illustrated at very low pressures by placing a nozzle on a garden hose. Where the water emerges from the nozzle, it is a cylinder of water. Where the stream is projected perhaps several meters through space, it breaks into divergent large droplets. This results from the interaction of the pump pressure, nozzle dynamics, surface tension of the water and inertial and viscous fluid forces and air entrainment in the stream. The distance that a cohesive stream may be directed in space is normally given in multiples of nozzle diameter. Typically, these interacting terms significantly reduce jet cohesion of the stream before it is projected a distance more than about 100 times the nozzle diameter.
The present disclosure incorporates a plurality of aligned holes in a plate or tubes within the nozzle construction upstream of the orifice. In addition to that, this disclosure utilizes a plurality of flexible fibers deployed between the flow straighteners just mentioned and the orifice. Ordinarily, the flow currents within the chamber of a nozzle immediately upstream the orifice are turbulent. As turbulence is reduced, the stream changes to streamline flow. This appears to reduce the required power to obtain the necessary pressure and flow rate. One theory of operation of the present structure contemplates that the flow is so controlled that it is not turbulent, and is in a region which is sometimes called streamlined flow. This further improves stream definition, meaning the stream has a narrow diameter at a greater distance from the orifice and delays along the stream the tendency of the stream to entrain air and break into droplets as a result of the fluid surface tension.